I just finished doing my math study guide for a test and there is one question that I don't know how to do. It is:

Question

f(x)=5-2x and g(x)=x^2=7x, find each value.
a. g(3)
b. f(2)+g(-1)
c g(2x)
I do not understand this at all, could someone explain this to me? Thank you.

Answer 1

So, this means you actually plug in the variables.

For example:
g(3) means for every x you see in g(x) you put a 3 in. Evaluate.

Answer 2

still don't get it

Answer 3

first of all , you have a typo in
g(x)=x^2=7x
I think you meant: g(x)=x^2+7x , since the + and the = are on the same key

you are given that
g(x) = x^2 + 7x
so you want g(3).
As Philip stated, wherever you had an x , now put in a 3
g(3) = 3^2 + 7(3)
= 9 + 21
= 90

so since f(x) = 5-2x
then f(2)+g(-1)
= 5 - 2(2) + (-1)^2 + 7(-1)
= 5 - 4 + 1 - 7
= -5

g(2x) , wherever I had an x, I now put in 2x
= (2x)^2 + 7(2x)
= 4x^2 + 14x